1. Field of the Invention
The present invention relates to an improved process for the preparation of zeolites, especially the zeolites of type A, having high cation exchange capacity, as well as the capacity for cation exchange at enhanced rate, and to the zeolites thus prepared and their use in detergent compositions/detergency.
2. Description of the Prior Art
For approximately the last decade this art has been replete with efforts to determine a proper substitute for sodium tripolyphosphate as a detergent builder to aid in detergency. Of necessity, such a substitute must:
(1) be an excellent cation exchanger or sequestrant, in particular of calcium and magnesium ions; PA1 (2) be a good dispersant; and PA1 (3) be capable of being mass produced in large quantities and at a low cost.
Obviously, it also must not be detrimental to the ecological environment.
Such efforts have in part focused on the zeolites as, on the one hand, they have already been otherwise used in detergent compositions and, on the other, in view of the advances to date attained in the field of synthetic zeolites.
Unfortunately, however, the available zeolites cannot compete with the sodium tripolyphosphates and, furthermore, while the requirements concerning the product are becoming more severe, the restrictions affecting processing are increasing.
Without being exhaustive, it can be said that certain major inroads have become discernible.
Even though the zeolites of type 4A, for example, may be produced at ambient temperature, industrial installations, for economic reasons, have typically adopted hot processes using at least one hot solution of at least one of the reagents. But problems involving the formation of gels and crystallization, and obviously the problem of the economy of energy arose, while at the same time the final products had to be cost competitive with the products they were designed to replace.
One of the most sensitive parameters is that of the formation of the gel and thus the quality of the contacting of the reagents, which is critical because it affects the quality of the final product.
For example, in European Pat. No. 13,417 it is proposed to use a double fluid nozzle system, wherein the reagents are separately introduced.
It has been proposed further, in European Pat. No. 17,013, to carry out multiple injection into a reactor, while maintaining a mean retention time of the reagents of less than 5 sec, but such multiple injection requires the use of a very long tube and entails a sinuous path.
In this case, intimate admixture apparently must be carried out after gelling.
It too is known that gels tend to obstruct their stream of flow, especially if same is winding and contains obstructions.
It has been further proposed in French Pat. No. 2,379,479, to perform a careful mixture in the shortest possible time, employing an inverted "Y" tube according to the examples, and wherein the time of mixing of the solutions varies from 6 to 7 min.
However, it would be redundant to emphasize the difficulties inherent in micro-mixing and macro-mixing systems in an industrial facility and the energy costs of such a solution.
Consideration too has been given to extending the time required for gelation.
Thus, in French Pat. No. 2,376,074 it is proposed to effect intimate admixture using relatively concentrated solutions (corresponding to an ultimate zeolite content in excess of 200 g/1) and at low temperature.
The results are said to be spectacular; however, the temperature of at least one of the reagents (for example, the aluminate) must be lowered, but it is produced at a relatively high temperature.
This of course makes any required heat transfer to the reaction medium much more difficult.
Cf. Chemical Abstracts, 97, No. 18, 147026z (1982), Chemical Abstracts, 97, No. 24, 200281g (1982) and Japanese Kokai No. 57-129,819 (1982), Chemical Abstracts, 96, No. 20, 164,989n (1982) and Japanese Kokai No. 57-03,713 (1982), and Chemical Abstracts, 98, No. 14, 109879t (1983) and Japanese Kokai No. 57-166,311 (1982).